1. Field of the Invention
This invention relates to manufacturing apparatus for use in photolithography, and more particularly to apparatus for to optimizing the quantity of photoresist applied to a substrate.
2. Description of Related Art
In photolithography, photoresist (also usually referred to in the art as resist and referred to both ways herein interchangeably) is deposited upon a work piece to be patterned by the photolithographic process. The expense of the quantity of photoresist used is the most or nearly the most expensive part of the cost of the process currently, depending upon prices of the materials used. Unfortunately, conventional resist spinners waste expensive resist material. In an application to manufacturing of semiconductor wafers, for example, a thick film of photoresist in the form of a puddle millimeters in height is delivered to cover most of a semiconductor wafer. Then the surplus photoresist material is spun off the semiconductor wafer surface, leaving an ultimate thickness of photoresist which is only on the order of several micrometers on the surface of the wafer. A very economical process currently requires 5 ml of photoresist material for each six inch diameter wafer.
U.S. Pat. No. 4,800,836 of Yamamoto et al for "Resist Coating Apparatus" neither introduces nor removes vapor from the chamber in which the resist is dumped on the substrate. No spraying is employed and there is no delay after application.
U.S. Pat. No. 4,416,213 of Sakiya for "Rotary Coating Apparatus" does not control the environment of the deposited resist.
U.S. Pat. No. 4,290,384 of Ausschnitt et al for "Coating Apparatus" suggests use of a mist but no spray and no spinning.
Japanese J6001248-A 85.01.19 (8509) Fujitsu, describes a resist coating method in which the atmosphere of resist solvent vapor is formed adjacent a semiconductor substrate and the resist is coated onto the semiconductor substrate. The solvent is discharged from one side of a porous disc. The resist is dropped onto the substrate. There is no spraying and no savings in resist material.
Japanese J02113518A 90.04.25 (9023) Mitsubishi Denki KK describes a resist coating device with a circular passage to introduce resist mist at a place surrounding the wafer on a spin chuck.
Japanese J02100314A 90.04.12 (9021) NEC Corp. describes an inner wall cup to coat a film of solvent or gas of photoresist.
Copending, commonly assigned U.S. patent application Ser. No. 07/784,290 filed Oct. 29, 1991 of Cardinali and Lin for "A Material Saving Resist Spinner and Process" describes resist coating with the spray-and-spin-in-vapor (SASIV) technique. With SASIV, the resist spin off is done in a vapor-rich environment so that spray resist application can be used to save resist material with a gain in thickness uniformity.
In the past resist thickness has varied even when employing the improvements in SASIV. That is a problem which needs to be overcome. Accordingly, there is a need to eliminate variations which occur with the SASIV process and the like.
In accordance with this invention, resist thickness is monitored and fine tuned in situ to achieve an accurate final thickness independent of variations of resist viscosity, vapor concentration, air flow, spin speed, and many other parameters.